Large-Scale Combat Operations Symposium – Detention in Non-International Armed Conflict


| May 15, 2023


Editor’s note: The following post highlights a subject addressed during an expert workshop that the Lieber Institute co-convened alongside Harvard Law School’s Program on International Law and Armed Conflict and the International Committee of the Red Cross, focusing on some of the legal issues arising in large-scale combat operations. For a general introduction to this symposium, see Winston Williams and Jennifer Maddocks’ introductory post.

Large-scale combat operations occur not only between States, but also between States and non-State actors. This is evident from recent non-international armed conflicts (NIAC), including the military operations to defeat ISIS in Syria and Iraq. While detention raises complex issues in any type of conflict, the detention of ISIS fighters in Syria highlights particularly intractable concerns due to ambiguities regarding the law of armed conflict (LOAC) that applies in this context.

This post explores some of the legal challenges that may arise when parties to a NIAC conduct conflict-related detentions, focusing on the detention of ISIS fighters and their families by the Syrian Democratic Forces (SDF). These detentions raise issues of LOAC compliance that concern not only the detaining authority (the de facto administration linked to the SDF) but also the coalition nations that support the SDF in its detention operations.

ISIS Detentions in Northeast Syria

Since the fall of Baghuz in March 2019, the de facto administration that controls areas of northeast Syria has detained thousands of former ISIS fighters. Many are held in makeshift prisons, often in conditions that human rights organizations describe as inhumane.

The administration holds an even greater number of ISIS families in camps for internally displaced persons (IDP). Many of the women are just as radicalized as the men, training their children to become the “Cubs of the Caliphate.” Due to the threat they pose, large numbers of these women and children are held in conditions tantamount to detention: they are not free to leave. Again, human rights organizations have decried the “appalling” conditions in which they live.

These allegations raise concerns regarding LOAC compliance. As a non-State party to a NIAC, the SDF is clearly bound by the provisions of common Article 3 to the Geneva Conventions. This, however, does not say a great deal about detention obligations. Common Article 3 articulates a duty to treat detainees “humanely, without any adverse distinction” and prohibits cruel treatment and torture. However, it does not define exactly what “humane treatment” means or whether this obligation could be violated by, for instance, holding detainees in overcrowded facilities. In its most recent commentary to common Article 3, the International Committee of the Red Cross (ICRC) provides some further clarification but stresses that the meaning of humane treatment “is context-specific and has to be considered in the concrete circumstances of each case” (para. 587). Therefore, considerable ambiguity remains.

Do the Parties to a NIAC have the Right to Detain?

A further area of uncertainty relates to the authority to detain in a NIAC and whether LOAC provides the parties to a NIAC with an implied right to detain. While the Third and Fourth Geneva Conventions provide an explicit legal basis for detention in international armed conflict, the law of NIAC includes no equivalent provisions. Some scholars therefore take the view that the authority to detain must be found elsewhere, either in domestic law or in a UN Security Council Resolution. Neither of these avenues, however, is open to the non-State party to a NIAC.

The question therefore arises whether detention by a non-State actor such as the SDF is inherently arbitrary, as lacking any legal basis. Other scholars and the ICRC (para. 765) take the view that this is not the case. They argue that by regulating detention, the law of NIAC includes a power to detain. Although the issue remains unsettled, it seems that through their support to the SDF’s detention operations, the States assisting the SDF as part of the global coalition against ISIS must implicitly accept that the SDF has a lawful basis to detain.

How Long Can Detainees be Held For?

Another important question relates to the length of detention in a NIAC. It is now over four years since the fall of Baghuz, when ISIS lost its last remaining territory in Syria. Many of the individuals detained at that time are still incarcerated, with little prospect of release or prosecution. So, assuming the SDF had a lawful basis to detain ISIS fighters and their families in 2019, does that basis endure today?

Given the absence of any specific guidance within the law of NIAC, one answer might be to look to the law of international armed conflict and conclude that detainees can be held until the end of active hostilities. But this raises a further question: is the NIAC between ISIS and the SDF still ongoing? Certainly, the intensity of the hostilities has weakened considerably since 2019. Yet, ISIS still poses a clear threat.

This continued threat is evident from the attempted prison break at a detention facility in the northeast Syrian city of Hasakah in January 2022. ISIS fighters attacked the facility from the outside, while detainees inside created chaos and sought to escape. According to the SDF, more than 100 of its members were killed in the attack. This incident demonstrates not only that ISIS as a group retains the capacity to launch complex attacks but also that ISIS detainees, when considered collectively, pose an enduring security threat that arguably justifies their continued detention.

However, doubts arise when considering the detainees on an individualized basis. Can it be said with certainty that every one of the thousands of ISIS affiliates detained, both in prisons and IDP camps, poses a threat to the SDF’s security? The only way that this can be determined is by conducting some form of detention reviews.

What Review Procedures are Required?

If review procedures are required for detentions in a NIAC to remain lawful, this raises further questions that the law of NIAC does not explicitly answer. For instance, how often should the reviews take place? Who should conduct them? Should the detainee have the right to participate?

According to the ICRC, individuals interned during a NIAC should have the right to challenge the lawfulness of their detention, with periodic reviews carried out “by an independent and impartial body” (para. 761). This body must be sufficiently independent “to function as an effective check against arbitrary or unlawful detention and have the power to order the release of detainees” (rule 11). Furthermore, the ICRC notes that mounting an effective challenge presupposes the fulfilment of certain procedural steps including providing internees with information regarding the reasons for their detention and ensuring they can seek and obtain additional evidence.

Although these guidelines make sense, compliance may present considerable practical difficulties for non-State actors engaged in detention operations. Regarding the SDF, conducting effective detention reviews for each of the many thousands of detainees held in prisons and IDP camps would require time, personnel, and resources that the non-State actor simply does not have at its disposal. In short, to conduct any form of review, the SDF would likely require considerable State support.

Even if that support is provided, however, a further question remains. A large proportion of the detainees are not Syrian nationals and many of their countries of origin are reluctant to repatriate former ISIS fighters and their families. So, if detention reviews conclude that non-Syrian nationals no longer pose a security threat and should be released, but their countries of origin will not repatriate, where should those individuals go? 

Considerations for Supporting States

Questions such as these are matters of concern not only to the SDF but also to members of the global coalition against ISIS that support the non-State actor in its detention operations. Certain members of the coalition, including the United States, have provided direct support to SDF detentions, for instance by funding security measures at detention facilities, constructing more secure prison structures, and training prison guards. In addition, coalition members have provided security support to the elements of the SDF that control the perimeter of al Hol IDP camp, including the provision of lights, cameras, and biometric enrollment equipment (p. 24-25).

When considered alongside the SDF’s potential LOAC violations outlined above, this support raises questions regarding the assisting States’ own international responsibility related to those breaches. A first consideration is whether the law of State responsibility might attribute the SDF’s conduct in violation of LOAC to a supporting State. For instance, if the SDF violated its humane treatment obligations under common Article 3 by holding detainees in severely overcrowded conditions, could this breach be attributed to one of the States that supports and enables the SDF’s detention operations, leading to that State’s international responsibility?

The most likely basis of attribution is that the SDF’s detention-related conduct was performed under the relevant State’s instructions, direction, or control (Article 8 of the International Law Commission’s Articles on State Responsibility (ASR)). However, ambiguities regarding the precise relationship between the SDF and the supporting States may lead to evidential hurdles in proving that this was the case.

If insufficient evidence is available to lead to attribution, it is nevertheless possible that the supporting States could bear international responsibility for their own contributions towards the SDF’s LOAC violations. Although the International Law Commission reached the view that States only bear responsibility for aid or assistance that facilitates another State’s international legal violations (Article 16 ASR), customary international law may be evolving to also hold States to account when they assist non-State actors to violate international law. In the Bosnian Genocide case, for example, the International Court of Justice indicated that the rule reflected in Article 16 may apply by analogy when States provide aid or assistance to a non-State actor (para. 419-420). Thus, if States provide detention-related support in the knowledge that this will assist the SDF to continue to hold ISIS detainees in violation of LOAC, those States could bear international responsibility for their contributions towards the relevant breaches.

The States that support the SDF could equally bear international responsibility for violations of their own obligations under common Article 1 to the Geneva Conventions. The duty to respect and ensure respect appears in identical form at the beginning of each of the four Geneva Conventions, yet its meaning is subject to considerable debate. For the ICRC and many scholars, this provision imposes both negative and positive duties on States to ensure that State and non-State actors engaged in conflict respect LOAC. From the ICRC’s perspective, this duty is even greater when a State develops support relationships, which enable the State to exert a greater influence over the actors it assists.

This broad interpretation of common Article 1 is not widely accepted by States. Nevertheless, the negative aspects of the duty are less contentious than the positive obligations that the ICRC asserts. Thus, it is clear from the ICJ’s judgment in Paramilitary Activities that States have a customary international law duty not to encourage non-State actors engaged in a NIAC to violate common Article 3 (para. 220). It would be anomalous if this duty did not also extend to States’ knowing facilitation of LOAC violations on the part of a non-State actor through the provision of assistance.

Concluding Thoughts

When thinking about large-scale combat operations, the principal focus of many Western democracies is, understandably, the conflict in Ukraine and the potential for future conflict with China. However, it is important that the world does not forget the many thousands of former ISIS fighters and their families who are detained in northeast Syria.

While for the time being States may feel able to turn a blind eye to the threats that former ISIS fighters and their families still pose, the time may come when this is no longer possible. If the situation in northeast Syria changes, for example because Türkiye resumes its invasion, thereby preventing the SDF from maintaining the prisons and IDP camps, we could see an ISIS resurgence. Given the number of children who have been indoctrinated with the group’s ideology, the future threat that ISIS may pose is real and potentially even greater than in the past.

If ISIS re-emerges with even a fraction of its past destructive capabilities, the legal issues highlighted in this post will return to the fore. Once again, it will be necessary to defeat the group and detain its fighters. Yet, detention in NIAC remains replete with ambiguity. Clarifying the LOAC standards that apply to detentions in this context thus remains an issue of pressing concern not only to the detaining authority but also to those States that act in its support.


Jenny Maddocks is an Assistant Professor in the Department of Law at the United States Military Academy, West Point.


Photo credit: Voice of America